Two types of distichiasis can be identified, acquired and congenital. In the acquired form, most cases involve the lower lids. Lashes can be fully formed or very fine, pigmented or nonpigmented, properly oriented or misdirected. The congenital form is dominantly inherited with complete penetrance. It can be isolated or associated with ptosis, strabismus, congenital heart defect, or mandibulofacial dysostosis. This defect may be related to the epithelial germ cells failure to differentiate completely to meibomian glands, instead they become pilosebaceous units.

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Pathophysiology

Distichiasis can affect the lower and upper lids (see following images). When these abnormal lashes come in contact with the cornea, they may cause severe irritation, epiphora, corneal abrasion, or even corneal ulcers.

This picture demonstrates distichiasis of the lower lid. From Principles and Practice of Ophthalmology by Jakobiec.